A field emission device emits electrons in response to an applied electrostatic field. Such devices are useful in a wide variety of applications including displays, electron guns and electron beam lithography. A particularly promising application is the use of field emission devices in addressable arrays to make flat panel displays. See, for example, the December 1991 issue of Semiconductor International, p. 11; C. A. Spindt et at., IEEE Transactions on Electron Devices, Vol. 38 (10), pp. 2355-63 (1991); and J. A. Costellano, Handbook of Display Technology, Academic Press, New York, pp. 254-57 (1992), all of which are incorporated herein by reference.
A typical field emission device comprises a cathode including a plurality of field emitter tips and an anode spaced from the cathode. A voltage applied between the anode and cathode induces the emission of electrons towards the anode.
Conventional electron emission flat panel displays typically comprise a flat vacuum cell having a matrix array of microscopic field emitter tips formed on a cathode of the cell ("the back plate") and a phosphor-coated anode on a transparent front plate. Between cathode and anode is a conductive element called a "grid" or "gate". The cathodes and gates are typically intersecting strips (usually perpendicular strips) whose intersections define pixels for the display. A given pixel is activated by applying voltage between the cathode conductor strip and the gate conductor strip whose intersection defines the pixel. A more positive voltage is applied to the anode in order to impart a relatively high energy (400-1000 eV) to the emitted electrons. See, for example, U.S. Pat. Nos. 4,940,916; 5,129,850; 5,138,237; and 5,283,000, each of which is incorporated herein by reference.
Diamonds are desirable field emitters. Early field emitters were largely sharp-tipped structures of metal or semiconductor, such as Mo or Si cones. Such tips, however, are difficult to make, have insufficient durability for many applications, and require relatively high applied fields (about 100 V/.mu.m) for electron emission. Diamonds, however, have structural durability and negative electron affinity--properties that make them attractive for field emission devices. Field emission devices employing diamond field emitters are disclosed, for example, in U.S. Pat. Nos. 5,129,850 and 5,138,237 and in Okano et al, Appl. Phys. Lett., Vol. 64, p. 2742 et seq. (1994), all of which are incorporated herein by reference. Flat panel displays which can employ diamond emitters are disclosed in co-pending U.S. patent application Ser. No. 08/220,077 filed by Eom et al on Mar. 30, 1994 and U.S. patent applications Ser. No. 08/299,674 and Ser. No. 08/299,470, both filed by Jin et al on Aug. 31, 1994. These three applications are incorporated herein by reference.
While diamonds offer substantial advantages as field emitters, it is highly desirable to employ diamond emitters capable of emission at voltages below those required by untreated diamonds. For example, flat panel displays typically require current densities of 0.1 mA/mm.sup.2. If such emission densities can be achieved with an applied voltage below about 25 V, then low-cost CMOS driver circuitry can be used in the display. This typically requires emission at fields below about 25 V/.mu.m. To achieve emission at such low fields, diamonds heretofore needed to be doped to n-type semiconductivity--a difficult and unreliable process. Accordingly, there is a need for improved diamond field emitters for low voltage emission.